The object of this proposal is to explore the usefulness of measurement of the frequency of the closure sounds of porcine bioprosthetic valves to determine if early and subclinical degeneration can be detected by this non-invasive method. The specific goal of the requested continuation of this investigation is to determine if changes of the frequency of the closure sound of bioprosthetic valves can be detected before clinical evidence of degeneration becomes apparent. It is important to know how soon changes of the frequency precede clinical evidence of degenerative changes. We have shown that the dominant frequency of heart sounds in patients with spontaneously degenerated porcine bioprosthetic valves is abnormally elevated when the degenerated valves are stiffened due to calcium or fibrosis. We also showed that the frequency content of the closure sounds of bioprosthetic valves is higher after five years of insertion than during the first 18 months. This suggests that stiffening progressively occurred. These observations were predictable and understandable on the basis that stiffening of a membrane increases the natural frequency with which it vibrates. Now that we know that the frequency of the closure sound of bioprosthetic valves increases with the duration of insertion, it would be useful for practical application of the method, to know how changes of the frequency relate to changes of the clinical status of individual patients, and to what extent measurable changes of frequency are predictive of future clinical degeneration of the bioprosthetic valve.